The rapidly expanding area of genetic testing has spawned some at-home testing kits, but at least one expert in the field writes in the journal Nature that the products promise more than they deliver.
Gene expert Craig Venter, who has been a key figure in the effort to sequence the human genome, conducted an experiment to test products from two genetic testing companies: Navigenics Inc., and 23andMe Inc.
Both companies sell testing kits online (US $399 for 23andMe, $999 for Navigenics). Both claim their tests provide an accurate picture of a person's future risk for diseases that are often inherited, such as breast cancer, celiac disease, and rheumatoid arthritis.
Customers fill the provided vials with saliva, and within a few weeks, their test results can be accessed over the Web.
Venter and colleagues put the products to the test by sending in DNA samples from five people to both companies.
What they found is that while the tests were highly accurate at generating raw genetic information, the analysis of what the results meant differed.
While the predictions of both tests for the risk of breast cancer, celiac disease, multiple sclerosis and rheumatoid arthritis were in agreement in all five customers, for nine other diseases, at least one of the test subjects got conflicting results.
"For seven diseases, 50 per cent or less of the predictions of two companies agreed across five individuals," Venter and colleagues write.
Those seven conditions included Crohn's disease, heart attack, lupus, prostate cancer, restless leg syndrome and type 2 diabetes.
Both testing companies scanned 500,000 to 1 million genetic variants. But discrepancies arose as to which variants they decided were actually markers of an increased disease risk.
With celiac disease, for example, the two companies agreed upon which genetic marker to look for to assess risk. But for other diseases, the companies relied on different markers.
What's more, even the DNA variants that have been identified so far that might increase risk for celiac disease account for only an estimated 35 to 40 per cent of the disorder's genetic basis.
Venter notes that the tests typically do not account for the positive genetic traits a person may have inherited that protect against disease. And of course, he notes, gene tests cannot account for healthy or unhealthy lifestyles.
He and his co-authors conclude that genetic scans as they exist today are generally unreliable and either cause customers needless worry or give them a false sense of security.
"Genetic testing can improve lifestyle choices and increase preventive screening," they write in Nature. "However, understanding of the genetic contribution to human disease is far from complete."
